External Flow on an Atrium

Description

External Flow around an Atrium is a complete, start-to-finish CFD training project that examines how horizontal wind interacts with an architectural atrium — a structure rooted in ancient Roman design and revived in modern multi-story buildings as a glass-roofed space for daylighting and natural ventilation. Atriums depend on two fundamental natural phenomena, the greenhouse effect and the chimney effect, and analyzing the external airflow around them is the first step toward designing them effectively.

In this simulation, an 8 m/s horizontal wind is driven across the atrium walls, producing the full range of external-flow behavior seen around bluff bodies: high-pressure stagnation zones, flow separation, recirculation, and local acceleration. At the urban scale, this matters because the wind around large buildings governs pedestrian comfort, natural ventilation performance, and how a structure interacts with its surrounding built environment — all central concerns of façade design, wind loading, and urban planning. By the end, you gain a reusable external-flow workflow that transfers to virtually any building-aerodynamics problem.

Methodology

The 3D external-flow domain (3.35 m × 2.21 m × 3.9 m) is constructed around the atrium in Design Modeler, sized to capture the wake and pressure field without artificially constraining the flow. The geometry is discretized into a refined unstructured mesh of roughly 1.95 million elements, with cell refinement concentrated near the building walls to resolve the boundary layer accurately.

On the solver side, a pressure-based, steady-state solver is selected — the natural choice for incompressible external aerodynamics. Turbulence is modeled with the RNG k-ε model together with standard wall functions, a combination well suited to the separated and recirculating flows that form around bluff bodies. Boundary conditions follow the standard external-flow setup: an 8 m/s velocity inlet, a 0 Pa gauge-pressure outlet, and stationary walls. Pressure-velocity coupling uses the SIMPLE scheme, with second-order discretization applied to pressure and momentum for improved accuracy. The domain is initialized with atmospheric pressure (101,325 Pa) and a uniform freestream velocity.

Analysis

Post-processing translates the converged solution into a clear physical picture of the flow. The results are presented as 2D and 3D contours of pressure and velocity, pathlines tracing the flow around and behind the structure, and velocity vectors on the XY plane that reveal separation and recirculation zones in detail. The pressure distribution over the building's wall surfaces is extracted directly, showing where the wind loads the structure most heavily and how the pressure field organizes around it.

Together these results let you identify stagnation, separation, recirculation, and acceleration regions and connect them back to real engineering decisions — façade design, pedestrian wind comfort, natural-ventilation potential, and structural wind loading.